A domestic steam iron has the capability to generate steam and to subsequently release this steam through outlet openings provided in the soleplate of the iron. The steam, which is applied directly to a garment being ironed, helps to diminish the ironing effort and to improve the ironing result.
To store the water that is to be released as steam, a steam iron is commonly fitted with a water reservoir. From there, a water channel guides the water either to a special steam chamber or directly to the soleplate of the iron, where it is heated and converted into steam. Thereafter, it may be released through the outlet openings in the soleplate. Normally, the generation and release of steam is desired only when the iron is in contact with a garment that is being ironed. Several arrangements to ensure such safe and energy-efficient steam iron behaviour have been disclosed in the art. In some of them, an iron is provided with a handle that can be used to control a valve that is disposed in the water channel leading from the water reservoir to the outlet openings in the soleplate of the iron. The handle is preferably operated intuitively, such that it is automatically forced into a position that corresponds to an open position of the valve when a user grips the iron in a manner that indicates an actual ironing activity. Intuitively operated handles commonly rely on the downward force that is exerted by a user's hand on the handle as the user steers the iron across the garment. When a user lifts the iron off of the garment, or when the iron is parked on an iron rest, no downward force is present, indicating that no actual ironing activity takes place. In the absence of a downward force, a biasing mechanism will push the handle into its stationary position, thereby ensuring closure of the valve such that no steam is released.
Research has shown that the forces exerted on a handle by ironing users range from less than 100 gf (0.98 N) to about 4 kgf (39 N). In addition, individual users do not display consistent force-exertion behaviour during a single ironing session either. Users of an iron with an intuitively operated handle may therefore not, or not at all times, automatically apply sufficient force to the handle to open the valve in order to effect the release of steam. From a user point of view, this corresponds to inconsistent iron behaviour: at the one moment the iron may release steam while at the other it doesn't, without a conscious choice being made by the user in between. Furthermore, any temporary or structural disruption of the steam supply due to a variable or consistently insufficient force may increase the ironing effort and worsen the ironing result.